Many internal combustion engines provided with a turbocharger have a waste gate valve, which opens and closes a bypass channel that connects an upstream part and a downstream part of a turbine to each other. If the supercharging pressure is higher than necessary, there arises a problem that knocking easily occurs. According to the prior art, the waste gate valve is designed to open when the supercharging pressure becomes equal to or higher than a predetermined value, thereby preventing the supercharging pressure from rising beyond the value.
Recently, there have been proposed techniques of actively controlling the opening and closing of the waste gate value with an actuator. For example, according to a technique disclosed in Japanese Patent Laid-Open No. 2006-274831, a fundamental opening of the waste gate valve is calculated from the throttle opening and the engine speed, a correction amount for the opening of the waste gate valve is calculated from the difference between a desired supercharging pressure and an actual supercharging pressure, and the actual opening of the waste gate valve is controlled to be a desired opening of the waste gate valve calculated from the fundamental opening of the waste gate valve and the correction amount for the opening of the waste gate valve.